Generally speaking, most of shift levers for use in bicycle have a reciprocating shift lever that directly tracts the shift cable for leading the derailleur to guide the chain for bias shift to each sprocket of different sizes as to change into different gear ratio.
Because such shift lever is shifted by hand to each different position so as to shift the derailleur into each different sprocket, the manipulation that is achieved entirely subject to the operator's experience and feeling will cause him failing to accomplish right position of the shift lever in different shifts. Therefore, such shift lever has to depend on a shift cable directly pulled by the shift lever while the shift lever needs to be fixed by frictional force produced from a fixing device so as to avoid shift skip as a result of shift lever pulled by the shift cable back to the original position after shifting.
For this reason, during shifting the operator has suffered a labor-consuming work since he not only has to sustain tension force due to the derailleur driven by the shift cable but also has to overcome frictional force imposed upon the shift lever by the fixing device.
Because of the aforesaid reasons, in the operation of such derailleur will cause the operator failing to accomplish right position of shifting and labor-consuming operation will also cause the operator getting exhausted.
To overcome the aforesaid defects, there are some shift levers in the market that have adopted ratchet device as shifting mechanism, such as the U.S. Pat. No. 5012692 "Change-speed Lever Apparatus For Use In Bicycle" as filed by Masashi Nagano, wherein a switch lever is used for leading a rachet to push the rachet wheel in forward rotation so as to pull the shift cable in movement, whereby a shifting speed is achieved by the derailleur, and multi-brake gear that engages the ratchet wheel serves to prohibit it from pulling back by the shift cable. For back shifting, the brake gear will be released by means of another switch lever, whereby the ratchet wheel can be pulled back by the shift cable and returned to the former shift depending on its own resilience.
For shifting forward of such shift lever, because of positioning function of ratchet wheel, the shift lever may proceed in right shifting operation and switching each block of the shift lever will cause the derailleur moving forward by one shift; switching a plural blocks will cause the derailleur moving forward by several shifts. In addition, upon accomplishment of each shifting operation, the return of the shift lever to the original position will make easier for shifting in bicycle. Besides, fixing the shift lever by means of brake-gear ratchet wheel can omit the past way of fixing the shift lever with frictional force so that shifting position of the derailleur becomes much more precise while no shifting operation resistance will occur increasingly.
However, because of some limits from the mechanism of such shift lever, when back shifting operation that brake gear disengagment from the ratchet wheel has caused the ratchet wheel to move back by one block, an auxiliary brake gear is required for holding up the ratchet wheel so as to prevent excessive pulling of the ratchet wheel by the shift cable otherwise the blocks of back shifting will be out of control. For this reason an operating trouble is hence caused since back shifting operation can be accomplished by one block only each time. Further because the shift cable of the shift lever is pulled by the ratchet wheel, shifting forward operation is almost like a direct pulling of the shift cable with the switch lever, whereby shifting forward operation remains a labor-consuming job.
In view of the aforesaid defects found in the conventional shift levers in respect of operation, the inventor has devoted himself to research and development and finally has achieved the present invention successfully based on experience in making and marketing related products over the years.